An example of a typical gas-turbine arrangement is shown in an abstract way in FIG. 1. The gas turbine comprises an air inlet 10 at one end followed by a compressor stage 11 in which incoming air is compressed for application to one or more combustors 12, which are distributed circumferentially around the turbine axis 13. Fuel is introduced into the combustors at 14 and is there mixed with a part of the compressed air leaving the compressor stage 11. Hot gases created by combustion in the combustors 12 are directed to a set of turbine blades 15, being guided in the process by a set of turbine guide vanes 16, and the turbine blades 15 and a shaft, forming the axis 13, are turned as a result. The turbine blades 15 in turn rotate the blades of the compressor stage 11, so that the compressed air is supplied by the gas turbine itself once this is in operation.
Part of a typical combustor is schematically shown in FIG. 2A. (FIG. 2B is a section along a line III-III shown in FIG. 2A.) The combustor is in four parts: a front-end part 20—a burner—, a swirler part 21, a burner pre-chamber part 22 and a combustion volume 23. Main fuel is introduced into the swirler part 21 by way of the front-end part 20 through a conduit 24, while pilot fuel enters the burner space through a conduit 25 having at its end a pilot-fuel nozzle 29 or via a series of injection nozzles or holes. The main and pilot fuel-flows are derived from a fuel-split valve 26, which is fed with a fuel supply 27 representing the total fuel supply to the combustor. The main fuel flow enters the swirler through a set of main-fuel nozzles (or injector) 28, from where it is guided along swirler vanes 101 of the swirler part 21, being mixed with incoming compressed air in the process. The resulting air/fuel mixture maintains a burner flame 30. The hot air from this flame enters the combustion volume 23.
A gas turbine will often comprise a number of such combustors, in which case the main and pilot fuel-flow distribution will usually be as shown in FIG. 3. A common supply of fuel for all combustors will be divided into a main fuel supply for all combustors and a pilot fuel supply also for all combustors.